Internal combustion engines have considerably lesser efficiency during partial load operation than during full load operation. Furthermore, due to the throttling losses, conventional gasoline engines, in particular, have markedly less partial load efficiency as opposed to diesel engines. Therefore, modern gasoline engines are being increasingly equipped with techniques for improving the partial load efficiency. In this connection, first of all, direct injection methods for gasoline engines must be mentioned that enable considerable increases in efficiency to be achieved by stratified operation or homogenous lean burn operation. Furthermore, methods for dethrottling the gasoline engine with partly or fully variable valve controls are used that enable the filling adjustment of the engine using opening times and closing times of the intake valves as well as using variable intake valve strokes.
Another possibility of achieving higher efficiency in multi-cylinder internal combustion engines exists in the shutdown of cylinders whereby a higher efficiency of the remaining cylinders can be achieved. Such a cylinder shutdown in series-production vehicles can be used preferably in high-cylinder engines, e.g. 8 or 12 cylinder engines by shutting down N/2 cylinders. In these engines, it is possible to ignite a sufficiently large number of cylinders having uniform angular ignition spacing even when shutting down half of the cylinders. Consequently, a comfortably acceptable running smoothness of the engine is achieved. In addition to methods that cut off only the fuel supply to the deactivated cylinders or interrupt the fresh air or the mixture supply over throttles, systems are known that carry out a method of shutdown by controlling the intake valves and exhaust valves. In the latter system, it is common to keep the intake valves as well as the exhaust valves closed after the combustion cycle in order to prevent the infiltration of crankcase gas through the filling remaining under excess pressure in the cylinder. The disadvantage here is that when restarting the deactivated cylinder, the combustion gas that is still present in the cylinder must first be expelled. This leads to a delay in the restart of the cylinder.
An engine control method is described in the patent application DE 42 92 543 C1 for a intake pipe injection engine in which only air is sucked into the deactivateable cylinders immediately before the shutdown and the combustion gas is prevented from being confined to the cylinders. When restarting a previously deactivated cylinder, the valve drive mechanisms that are associated with the deactivateable cylinders are released from the stoppage in the valve operation and are thus restarted. Furthermore, a rapid-acceleration detecting unit detects whether or not the engine is operating in a region of rapid acceleration. If the engine is operating in a region of rapid acceleration, then a preliminary fuel injection into the deactivateable cylinders is carried out. In a normal state, the fuel injection is started after the valve operation is restarted, that is, after only air is sucked into the deactivateable cylinders. Due to the intake pipe wall film effect during the indirect injection, an additional fuel mass that can be determined with difficulty is located in the cylinder during the restart of the previously deactivated cylinder. This leads to a high imprecision when metering the correct fuel mass for the required set air ratio during restart. In addition, a small quantity of fuel and oil enters into the cylinder combustion chamber via the blow-by depending on the duration of the shutdown phase. This leads to an additional change in the mixture composition.
Furthermore, the patent application DE 195 46 549 C1 describes a method of restarting a cylinder after an intake cycle and prior to an exhaust cycle. In order to prevent an undesired cooling of the combustion chamber, the patent application suggests that hot exhaust gas should remain in the deactivated cylinder during the shutdown phase.
In order to prevent an undesired torque jerk when shutting down and/or restarting cylinders, the patent application EP 1 298 300 A2 proposes to reduce the power of the cylinders to be shut down during the partial engine operation before shutdown and to simultaneously increase the power of the cylinders still running. When restarting the cylinders, their power is increased while the power of the cylinders still running is reduced or kept constant. Since a loss of gas can occur in a deactivated cylinder due to leakages, the patent application DE 33 16 446 A1 suggests that the intake valve be opened briefly even in a deactivated cylinder.